1. Field of the Invention
The present invention relates to a material for forming an optical waveguide through which a light signal can be propagated, and an optical waveguide made of the material and a method for manufacturing the optical waveguide.
2. Description of the Related Art
As the technology in an IC (Integrated Circuit) and an LSI (Large Scale Integrated) circuit progresses, their operating speed and scale of integration have been being improving, thereby rapidly promoting, for example, an enhancement in performance of a microprocessor and an increase in capacity of a memory chip. Hitherto, transmission of information over relatively short distances, for example, between boards in a device or between chips on a board is carried out mainly via an electric signal. In order to further improve the performance of an integrated circuit in the future, it is necessary to increase the transmission rate of a signal and the density of signal wiring. In the electric signal wiring, however, it is difficult to increase the transmission rate of a signal and the density of signal wiring, and a problem of a signal delay due to a time constant of CR (C: electrostatic capacitance of the wiring and R: resistance of the wiring) of the wiring arises. Since an increase in transmission rate of the electric signal and an increase in density of the electric signal wiring cause EMI (Electromagnetic Interference) noises, it is indispensable to take countermeasures against the problems.
Attention is being paid to optical wiring (optical interconnection) as means for solving the problems. The optical wiring is considered to be applicable to various situations such as the interconnection between devices, between boards in a device, or between chips on a board. For transmission of signals over relatively short distances such as transmission between chips, an optical transmission communication system in which an optical waveguide is formed on a substrate on which chips are mounted and is used as a transmission line is suitable.
Hitherto, an optical waveguide of this kind is made of an inorganic glass material such as quartz. In the case of forming an optical waveguide by using the inorganic glass material, however, heat treatment at high temperatures has to be performed. Consequently, the optical waveguide cannot be formed on a substrate such as a semiconductor substrate or a plastic substrate which cannot be subjected to the heat treatment at high temperatures.
On the other hand, in recent years, an optical waveguide made of a high polymer material has been proposed (see Japanese Unexamined Patent Application Nos. 7-56030 and 7-159630) and is becoming commercially practical. High polymer materials can be processed easier as compared with inorganic materials. A device of a larger area and in the form of a film can be easily formed by using a high polymer material. The high polymer materials have various advantages such as a wide range of applications owing to their flexibility, and easy adjustment of a refractive index. Among the high polymer materials, an ultraviolet-setting resin is a material which is cheap and can be produced in quantities. An ultraviolet-setting resin is therefore expected as a material for optical waveguide. A known example of the ultraviolet-setting resins is an epoxy resin.
An optical waveguide made of an epoxy resin is generally formed by applying the resin on a supporting substrate, selectively exposing the resin, and performing a developing process of wet-etching uncured portions in the resin.
Since the polymerizability of an epoxy resin is low, however, when the optical waveguide is formed by using an epoxy resin, there is a problem such that a large amount of energy is necessary to cure the resin and this deteriorates production efficiency.
Since an epoxy resin has low solvent resistance, at the time of wet-etching the uncured portion in the resin, the cured portion is also dissolved. This causes a problem such that the optical waveguide cannot be formed in a desired shape.
Japanese Patent Publication No. 2679586 discloses an activated energy beam curing composition comprising a compound having two or more oxetane rings per molecule, a compound having one or more oxirane rings per molecule, and a cationic polymerization initiator. However, there is no disclosure as to whether the composition can be used as a material of an optical waveguide. If the composition can be used as a material of an optical waveguide, the publication does not clarify conditions under which the composition can be used.
The present invention has been achieved in consideration of the problems and its object is to provide a material for an optical waveguide, having high polymerizability and high solvent resistance, and an optical waveguide made of the material and a method for manufacturing the optical waveguide.
According to the invention, there is provided a material for an optical waveguide through which a light signal can propagate, comprising: a first compound having an oxetane ring; and a second compound capable of initiating polymerization by a chain reaction.
According to the invention, there is provided an optical waveguide through which a light signal can propagate, wherein the optical waveguide is formed by using a material for an optical waveguide comprising a first compound having an oxetane ring and a second compound capable of initiating polymerization by a chain reaction.
According to the invention, there is provided a method for manufacturing an optical waveguide through which a light signal can propagate, the method comprising: a step of forming an organic material layer on a supporting substrate by using a material for an optical waveguide comprising a first compound having an oxetane ring and a second compound capable of initiating polymerization by a chain reaction; a step of selectively exposing and curing the organic material layer by selectively irradiating the organic material layer with an energy beam; and a step of forming an optical waveguide by a developing process of removing an uncured portion in the organic material layer.
Since the material for an optical waveguide of the invention comprises the first compound having the oxetane ring, it has high polymerizability and high solvent resistance.
In the optical waveguide according to the invention, a light signal enters from one end face, propagates through the optical waveguide and goes out from the other end face. The optical waveguide comprises the material for an optical waveguide of the invention, which contributes to high solvent resistance.
In the method for manufacturing the optical waveguide according to the invention, the organic material layer made of the material for an optical waveguide of the invention is selectively irradiated with an energy beam and the irradiated portions are cured. After that, the uncured portions in the organic material layer are removed by the developing process, thereby obtaining the optical waveguide.
Other and further objects, features and advantages of the invention will appear more fully from the following description.